This invention relates to improvements in computer graphics systems and, more particularly, to a delineating method and apparatus employed in a computer graphics system, special effects device or a video game equipment employing a computer.
It is common practice in the prior art, as for example in a TV game machine for household use, personal computer or a computer graphics system, a picture generating device for generating data of a picture outputted and displayed on a television receiver, monitor receiver or a cathode ray tube (CRT), that is data of a display output picture, to provide a dedicated delineating device between a central processing unit (CPU) and a frame buffer for enabling high-speed processing.
In this regard, when generating a three-dimensional picture by the picture generating device, the CPU does not directly access a frame buffer, but performs geometric processing, such as coordinate transformation, clipping or light source calculations, for defining a three-dimensional shape as the combination of polygons, such as triangles or a quadrangle, to generate instructions for delineations in order to transfer the generated instructions for delineation to the delineating device.
By way of illustration, for generating a picture of a three-dimensional object, a CPU may first define the object as a combination of polygons.
The CPU generates delineating instructions corresponding to these polygons for delineating the three-dimensional picture derived from the object and transfers the delineating institutions to the delineating device.
The delineating device interprets the delineating instructions sent from the CPU to find the colors of all pixels making up a polygon and Z-values specifying the depth from the color data of the apex points and the Z-values. The delineating device then performs rendering processing for writing the pixel data in the frame buffer to delineate a figure in the frame buffer.
The Z-value is the information specifying the distance from the viewing point in a direction along the depth.
When delineating a polygon from the various polygons making up the object, the delineating device first interprets the delineating instructions from the CPU to find Y-coordinates of apex points of the polygon in order to find the maximum value Y.sub.max and the minimum value Y.sub.min of the Y-coordinate values.
The delineating device rounds up and rounds down the minimum value Y.sub.min and the maximum value Y.sub.max of the Y-coordinate values in order to find the horizontal lines of pixels intersecting the polygon. The delineating device finds the points of intersection of the polygon with these horizontal lines of pixels.
The delineating device then rounds down the values of the X-coordinates of the points of intersection in order to find the maximum value X.sub.max and the minimum value X.sub.min of the pixels comprised in the polygon.
In the horizontal pixel lines, the delineating device writes the pixels comprised within a range from the minimum value X.sub.min to the maximum value X.sub.max of the X-coordinate values for every horizontal pixel line in the frame buffer.
However, as a result of the polygon being delineated on a frame buffer by the above-described delineating device, a boundary edge of the polygon is jagged. This jagged state of the boundary of the polygon is referred to hereinafter as "jaggies."
The above-described delineating device may employ either a sub-pixel method or a background mixing method for eliminating the jaggies.
The sub-pixel method resides in delineating a polygon on the frame buffer with resolution higher than the actual display resolution and passing the polygon through a low-pass filter for decreasing the resolution to the actual display resolution for removing the jaggies.
However, with the delineating device employing a sub-pixel method, since delineation needs to be carried out with a resolution higher than the actual display resolution, it is necessary to provide a frame buffer having a resolution higher than actual display resolution, thus increasing the hardware scale of the delineating device.
On the other hand, the background mixing method finds the ratio of the inside portion of a polygon contained in a pixel when the real edge of the polygon intersects the pixel and to mix the color of the polygon with the background color by this ratio for removing the jaggies.
However, with the delineating device employing the background mixing method, the color of the background, which should not be visible, is mixed with the edge color thus producing the bleeding of the background color.
Accordingly, there has been a long existing need in the art for enhanced image data processing wherein delineation is accomplished with minimal hardware requirement and which avoids jaggies and bleeding of background color. The present invention clearly fulfills these needs.